Meeting Abstract

146.2  Monday, Jan. 7  Different neural target tissues mediate melatonin-dependent regulation of the RFamides, kisspeptin and gonadotrophin-inhibitory hormone, in Siberian hamsters HENSON, J.R.*; FREEMAN, D.A.; Univ. of Memphis; Univ. of Memphis jrhenson@memphis.edu

Siberian hamsters exhibit seasonal rhythms in physiology and behavior that aid in their ability to cope with annual changes in the environment. These include intra-annual changes in reproductive function, body mass, energy balance, and pelage coloration that are driven by changes in day length. For example, short day lengths inhibit, whereas long day lengths stimulate the reproductive axis. Day length is encoded by the duration of nocturnal pineal melatonin (Mel) secretion, which acts at several neural Mel target tissues to alter reproduction via changes in the release of hypothalamic gonadotrophin-releasing hormone (GnRH). Interestingly, GnRH neurons do not express Mel receptors, suggesting that regulation of GnRH by Mel is mediated by factors upstream of GnRH neurons. We assessed the effect of Mel on two up-stream GnRH regulators, kisspeptin (Kiss1) a positive regulator, and gonadotrophin-inhibitory hormone (GnIH, also termed RFRP-3) a negative regulator. We extended the Mel rhythm locally within specific target tissues in male hamsters housed under long day length by employing Mel-containing cannulas implanted into either the suprachiasmatic nucleus (SCN) or the nucleus reuniens (NRe). Extending the Mel duration at either target tissue elicited the expected testicular regression, and evoked site-specific effects to the RFamides. Mel administered to the SCN resulted in a reduction in Kiss1-immunoreactivity (-ir) in the anteroventral periventricular nucleus and Mel localized to the NRe resulted in a reduction of GnIH-ir in the dorsomedial hypothalamus. The results indicate that these two RF-amides are regulated independently by Mel acting at distinct target tissues.